Centrifuge

ABSTRACT

A centrifuge for separating contaminants from a liquid, such as lubricating oil. The centrifuge includes a rotating cylindrical sleeve assembly open at one end and provided with a readily removable and replaceable annular particle receiving and entrapping sleeve. The centrifuge includes a positive displacement-type pump operable to discharge decontaminated fluid from the centrifuge at a rate at least equal to the rate at which contaminated fluid is fed into the centrifuge, to thereby achieve nonflooded operation and to permit the separation of entrained air from the lubricant.

United States Patent [72] Inventor Harold DouglasSeielstad, Jr. 2,135,213 6/1964 Smith etal 233/24UX Birmingham, Mich. 3,347,380 10/1967 Alsobrooks 233/2X [2]] Appl. No. 809,113 3,348,767 10/1967 Femey 233/2X (22] Filed Mar. 21,1969 3,377,019 4/1968 Cox 233/2 [45] Patented Mar. 30,197] 3,385,517 5/1968 Cannon 233/2 [73] Assrgnee glidwiegafieailriildustnes Corporation Primary Examiner Jordan Franklin c Assistant Examiner-George H. Krizmanich Att0rney-John G. Batchelder [54] CENTRIFUGE l3 Clams u Drawmg Flgs' ABSTRACT: A centrifuge for separating contaminants from a [52] v US. Cl 233/2, liquid, such as lubricating oil. The centrifuge includes a rotat- 210/ 1 68, 210/416, 233/24 ing cylindrical sleeve assembly open at one end and provided llll. a readily removable and replaceable annular particle Fleld of Search receiving and entrapplng leeve The centrifuge includes a 24; 210/168, 486, 416, 483, 484, 496, 49 itive displacement-type pump operable to discharge 56 R f Cxed decontaminated fluid from the centrifuge at a rate at least l e erences I equal to the rate at which contaminated fluid is fed into the UNITED STATES PATENTS centrifuge, to thereby achieve nonflooded operation and to 3,135,21 1 6/ 1964 Pezzillo 233/ 24UX permit the separation of entrained air from the lubricant.

I08 "6 I04 I02 20 I00 80 42 IIB 9o 74 97 92 A I I ffgfi? as 67 Tl 58 I22 I26 78 3s 58 as 34 as Urdu a? 60 Patented March 30, 1971 3,512,582

4 Sheets-Sheet 1 INVENTOR. HAROLD D. SEIELSTAD, JR.

BY SETTLE,'BATCHELDER a OLTMAN.

Patented Mafch 30, 1971 3 3,572,582

4 Sheets-Sheet 2 INVLL'N'RJR.

HAROLD D. SEIELSTAD, JR. BY

SETTLE, BATCHELDER a OLTMAN.

ATT'YS.

Patented March 30, 1971 3,512,582

4 Sheets-Sheet 3 INVENTOR.

HAROLD D SEIELSTAD,JR.

BY SETTLE, BATCHELDER 8 OLTMAN.

ATT YS.

Patented March 30, 1971 3,572,582

4 Sheets-Sheet 4.

INVENTOR.

HAROLD D SEIELSTAD, JR.

SETTLE, BATCHELDER a (lTMAN.

ATT'YS.

camrrues BACKGROUND OF THE INVENTION The separator of the present invention was specifically designed for removing contaminants from lubricating oil employed in the lubrication system of jet engines. Conventionally, such engines in the past have employed static or barrier type filters-i.e. filter screens-to filter the lubricant in their recirculating lubrication system. While filters of this type have, in the past, proved generally satisfactory in aircraft usage, they are not entirely without drawbacks. Employment of jet engines in stationary applications revealed a further drawback to the static or barrier-type filter when it was found that engine bearing life in the stationary applications was drastically reduced due to the fact that in the stationary application, the engines were run at high throttle settings a substantially greater portion of the time than is the case in aircraft usage. The increased operating pressures and temperatures encountered by the lubricant at high throttle settings of the engine resulted in an increase in breakdown of the lubricating oil and synthetic additives which produce fine microscopic particles tending to shorten engine bearing life.

Static or barrier-type filters possess two basic limitations in systems of this type. First the barrier-type filter produces a pressure drop in the system which inherently increases as the filter collects dirt particles. There is a definite limitation in the amount of particles which can be collected before cleaning or replacement of the filter element must occur. Second, particularly in aircraft engine lubrication system, the system must be operable to function over a wide range of operating fluid temperatures, for example, typically from -6 F. to 350 F., and the viscosity of the lubricating oil and hence its flow characteristics through filter screens changes drastically over this range of temperatures.

The centrifugal separator presents the opportunity of overcoming the problem of pressure drop inherently present in a barrier-type filter since the centrifugal separator acts essentially as a pump and can, in fact, be operated to produce a pressure rise across the separator. Further, in a centrifugal separator, the dirt particles are withdrawn from the lubricant flow path, rather than collected in the flow path as in a barriertype filter. Further, the centrifugal separator affordsan opportunity for further providing for the separationof entrained air bubbles from the fluid, which is not possible in a barrier-type filter.

Significantly finer filtration with a structure of a given size and weight-both critical in aircraft engine design-is obtained with a centrifugal separator than would be possible with barrier-type filters. Further, because the separated particles are removed from the flow path, the period of operation of the system before cleaning or replacement of the particle trapping element is required is increased by a factor of 10 or more over barrier-type filters.

SUMMARY OF THE INVENTION The centrifugal separator of the present invention has been designed not only to overcome the problems outlined above, but to further operate at a minimum power requirement, to retain and collect containment particles in a manner such' that removal of the particles can be swiftly and efficiently accomplished and to be of a minimum size andweight for use in aircraft environments. To this end, the separator of the present invention employs a relatively small diameter cylindrical basket or shell which is driven to rotate at relatively high speeds-Le. in the order of 7,000 r.p.m. The basket takes the form of a cylindrical shell, open at one end and within which is removably mounted a hollow tubular sleeve which is adapted to receive and entrap solid particles or particles denser than the fluid. The cylindrical shell is mounted within a closed casing having a readily removable cover plate adjacent the open end of the shell so that, upon removal of the cover plate, the annular particle collecting sleeve can be readily extracted and replaced. To reduce the power requirements for driving the shell in rotation, and to further provide a means for also separating air from the incoming mixture, the separator is provided with its own pump to enable the separator to operate in a nonflooded condition. The capacity of the pump is such that decontaminated oil passing from the separator basket is pumped from the separator casing at a rate at least equal to that at which contaminated oil is fed into the separator. By maintaining a given flow rate through the centrifugal separating elements, an air vent can be led into the axis of the unit to permit air separation, and the confining of the flow through the centrifugal separating element to a relatively narrow annular region further provides maximum separating efi'lciency because of the relatively small radial distance the particles must travel before encountering the particle-cntrapping sleeve.

Three embodiments of particle receiving sleeves are disclosed, all having the common feature of being operable to receive particles relatively easily under the centrifugal action of the separator, but at the same time inhibiting movement of the particles within the sleeve once the particles have been received. In addition to entrapping the particles, the inhibiting movement of particles within the sleeve minimizes slumping of the entrapped mixture when the separator is stopped to inhibit the flow of particles to the lower portion of the sleeve, which is mounted for rotation about a horizontal axis, this latter action creating a rotary imbalance of the assembly upon subsequent starting up of the separator.

Other objects and features of the invention will become apparent from the following specification. In the Drawings:

FIG. I is a detail cross-sectional view taken on a substantially vertical central plane passing through a separator embodying the present invention; 7

FIG. 2 is a side elevational view of the main body casting of the separator of FIG. 1;

FIG. 3 is a detail cross-sectional view taken approximately on line 3-3 of FIG. 2;

FIG. 4 is a detail cross-sectional view taken on line 4-4 of FIG. 2;

FIGS. 5, 6 and 7 are detail cross-sectional views of a pump employed in the separator of FIG. I taken respectively on lines 5-5, 6-6 and 7-7 of FIG. I;

FIGS. 8 and 9 are detail partial cross-sectional views, taken respectively on axial and radial planes, of a modified form of particle-entrapping sleeve; and

FIGS. I0 and II are detail partial cross-sectional views, taken respectively on axial and radial planes, of still another modified form of particle-entrapping sleeve.

Referring first primarily to FIGS. 1 and 2, the separator of the present invention includes a closed casing defined in part by a main body casting designated generally 20, the casing alone being shown in side elevation in FIG. 2. As best seen in FIG. I, the main casting 20 is formed with two main openings, at 22 and 24, the opening 22 in the assembled structure being closed by a mounting adapter member designated generally 26 which is fixedly secured to casting 20 as by a plurality of bolts 28 (FIG. 1) which are threaded into bosses 30 (FIG.' 2) formed in casting 20. An end cap designated generally 32 is detachably mounted within opening 24 in casting 20 to close the opening, end cap 32 being held in assembled relationship by a circumferentially extending clamping strap M. Strap 34 includes a channel-shaped inner member 36 having inclined sidewalls 38 which engage complementary inclined surfaces 40 on casting 20 and end cap 32 to wedge the end cap into firm seated engagement with casting 20 when strap 34 is cir cumferentially tightened in position by a threaded connection between the opposite ends of the strap, the threaded connectionbeing indicated at 42 in FIG. 1. v

The interior of casting 20 is divided into a main internal chamber 44 and a pump chamber 40 by an integrally cast partition 48, the two chambers communicating with each other by means of an opening 50. 5

Referring now particularly to FIG. 1, a main drive shaft 52 is rotatably mounted as by bearings 54 and 56 to extend axially through adapter member 26 and pump chamber 46. Shaft 52 may be driven in rotation either by a separate drive motor supplied for this purpose or by means of a suitable gear coupling driven by the engine whose lubricating fluid is to be separated by the separator. Since the actual source of power to shaft 52 may take either of the two foregoing forms, the prime mover of shaft 52 is indicated schematically at 58.

A main drive gear 60 is fixedly mounted upon shaft 52 and meshes with a driven gear section 62 fixedly secured to or integrally formed with a second shaft 64 rotatably supported as by bearings 66 and 67 and extending axially through the main internal chamber 44. For convenience in description, that end of shaft 64 at which driven gear 62 is located will be referred to as the axially forward end of shaft 64 and, at this end of the shaft, an enlarged diameter section 68 encloses an inlet chamber 70 formed in the interior of the forward end of shaft 64. A stationary inlet nozzle 72 projects axially into the forward end of inlet chamber 70 to conduct fluid to be centrifuged from an inlet conduit 74 into the interior of chamber 70, nozzle 72 being provided with radially directed openings such as 76. A reduced diameter passage 78 extends from the rearward end of the inlet chamber 70 coaxially through the entire length of shaft 64.

A cup-shaped, generally cylindrical shell assembly designated generally 80 is eoaxially mounted upon the exterior of shaft 64 by the engagement between an end wall section 82 on shell 80 and a seat section 84 on the exterior of shaft 64 at the rearward end of enlarged diameter section 68. In addition to the engagement between end wall 82 and enlarged diameter section 68, shell 80 is supported upon shaft 64 by an inner sleeve member 86 circumferentially engaged with shaft 64 as at 88 at its rearward end and having a channel-shaped flange 90 at its forward end which receives an annular rearwardly extending hub 92 which is integrally formed on end wall 82. Inner sleeve 86, hub 92 and shaft 64 are rotatively interlocked to each other as by pins 94 received in complementary semicircular recesses in hub 92 and flange 90 and which project axially into slots 97 on the shoulder at the rearward end of enlarged diameter section 68. The abutting engagement between the rearward end of sleeve 86 and bearing 67 maintains the axial relationship between shell 80 and shaft 64.

Fluid to be centrifuged flows from inlet chamber 70 into the interior of cylindrical shell 80 through openings 96 in enlarged diameter 68 into radially outwardly and axially rearwardly inclined impeller passages 98 which extend through hub portion 92 of end wall 82. The liquid flows axially rearwardly through shell 80, and during its passage through the shell is subjected to a centrifuging action by virtue of the rotation of the shell. Dirt particles in the fluid are centrifugally forced radially outwardly and are received and entrapped within an annular sleeve assembly designated generally 100 which is detachably mounted in the interior of cylindrical shell 80. Sleeve 100 includes an annular outer shell 102 of imperforate sheet metal having a reversely bent annular flange 104 at its forward end and secured, as by tack welding or adhesive bondings at its rearward end to an annular ring member 106. An end ring 108 is employed to clamp a tubular section of wire mesh screen 110 to lip 104, the forward end of screen 110 being seated in a notch 112 in ring 106. The annular space between tubular screen 110 and outer shell 102 is filled with a flow inhibiting fibrous material 114, which may take the form of stainless steel wool suitably immobilized to prevent strands from breaking loose.

Annular sleeve 100 is held in position in the interior of shell 80 by the engagement of end ring 108 with an annular seat 116 formed on end wall 82, the sleeve 100 being maintained against a split ring 118 seated within an annular notch 120 in shell 80, axially engaged against annular ring 106, by means of a wave-type compression spring 121 positioned between the end wall 82 and the end ring 108.

The annular sleeve 100 is thus readily accessible for replacement or cleaning, since it may be easily removed from the assembly by unclamping strap 34, removing end cap 32,

and removing the split ring 118; the compressed wave-type spring 121 forces the sleeve assembly out of the cylindrical shell 80. The openings in tubular screen permit a mixture of lubricant and solid particles to flow centrifugally into the entrapping fibrous material 114. The fibrous material acts to entrap the particles, and serves a further function of inhibiting slump of the sludgelike mixture accumulated within the sleeve. Slump" refers to the settling action of sludge within sleeve 100 when the centrifuge is stopped, the mixture tending to flow to the bottom of the sleeve, and thus creating a rotary imbalance when the centrifuge is again started up.

ln order to increase the separating efficiency, the axial flow path of lubricant is confined to a relatively narrow annular path 73 extending along the inner side of annular sleeve 100 by an annular skirt 122 formed on inner sleeve 86. The rearward end of skirt 122 is formed with a plurality of axially extending slots 124 which serve as a means for mounting axially extending flow directing vanes 126 which project radially outwardly from skirt 122.

Lubricant flows axially from the open rearward end of cylindrical shell 80 into the internal chamber 44 and thence downwardly through opening 50 into pump chamber 46.

An internal gear pump designated generally 128 is mounted within pump chamber 46 to pump centrifuged fluid from the main internal chamber 44 out of the casing. Pump 128 is a commercially available pump manufactured and sold by W. H. Nichols Company of Waltham, Mass, Model 6170. Pump 128 includes an inlet housing 130 and an outlet housing 132 which fit snugly into pump chamber 46. Outlet housing 132 is fixedly secured to main body casting 20 as by bolts 134. lnlet housing 130 is rotatively locked to outlet housing 132 as by a pin 136 and is axially biased against outlet housing 132 by a compression spring 138.

As best seen in FIGS. 1 and 5 through 7, inlet housing 130 is formed with a generally arcuate opening 140 which passes through an end wall 142 of the housing to open into an eccentrically located internal chamber 144 in the interior of inlet housing 130. As best seen in H6. 6, inlet housing 130 is circular in transverse cross section and is mounted within main body casting 20 in concentric relationship to main drive shaft 52, chamber 144 being circular in transverse cross section and eccentrically located with respect to shaft 52. An internal gear element 146 is rotatably mounted within chamber 144 and is meshed with a driving gear element 148 rotatively locked to shaft 52.

As best seen in H6. 7, outlet housing 132 is formed with a pump outlet opening 150 of generally arcuate shape which communicates with an outlet passage 152 which passes tangentially outwardly through outlet housing 132 and opens into an outlet passage 154 formed in main body casting 20. As best seen in FIGS. 2 and 4, outlet passage 154 passes to the right along the outer side of chamber 46 to an outlet opening 156. The normal flow of fluid from chamber 44 thus is axially to the left through pump 128 as viewed in FIG. 1 then radially outwardly through passage 152 and pump outlet housing 132 into the left-hand end of passage 154 and thence (FIGS. 2 and 4) to the right along the outer side of chamber 46 to outlet opening 156.

The capacity of pump 128 is selected to be at least equal to the rate of flow of contaminated liquid into the inlet 74 so that a continuous and steady flow is maintained through the centrifuge to prevent it from operating in a flooded condition. Preferably, the rate of flow of fluid through the centrifuge is maintained by pump 128 so that fluid passing axially through the separation chamber is confined to a relatively narrow annular region having an inner radius approximately corresponding to that of skirt 122. The relatively thin annular flow region assures that all entrained dirt particles are carried quite close to screen 110 to efficiently expose the particles to the entrapping characteristics of the sleeve 100.

Referring particularly to F105. 2 through 4, a bypass passage is formed in main casting 20 between the main internal chamber 44 and outlet passage 154. A one-way check valve 162 is mounted in and controls flow through passage T60 to permit the flow of fluid from chamber 44 into outlet passage 154. The purpose of passage 160 and check valve 162 is to provide for a bypass of pump 128 in the event of a malfunction to the pump or pump driving mechanism.

Alternatively, a one-way relief valve could be mounted in place of the bypass valve 162 to permit flow through passage 160 from outlet passage 154 to the main internal chamber 44; The purpose of such a valve would be to relieve excess pressure generated by pump 128 in the event of blockage of the flow of fluid out of the centrifuge.

Referring now to FIGS. 8 and 9, there is shown an alternative form of sleeve 100, designated generally. 100a. Sleeve 100a consists simply of a cylindrical thin metal shell 170 formed with reversely bent annular retaining lips 172. at each axial end which serve to retain within the sleeve a tubular element 174 of a porous, spongelike particle entrapping material. The material from which tube 174 is made preferably possesses a reasonable degree of firmness to the extent that it possesses some degree of resilience but does not compress to any substantial extent under the radially outward pressure exerted against it by the centrifugal force on the fluid flowing through it during operation. Preferably, tube 174 is a foamed synthetic or plastic material, although it may also be formed from porous sintered metallic or ceramic material.

Material of this general type provides both a particle-entrapping and flow inhibiting action in that the centrifugal forces which drive the particles into the material of tube 174 during operation of the centrifuge are far greater thanthe gravitational forces acting on the particles when the sleeve 100a is not rotating.

In FIGS. 10 and 11, still another form of sleeve, designated generally 10% is disclosed. Sleeve ltlOb includes an imperforate thin metal sleeve 180, within which a plurality of axially extending ribs 182 are fixedly mounted. A relatively coarse mesh wire screen is formed into a tube 184 and a tubular section of resilient'sheet material 186 is fitted around the outer periphery of the wire mesh tube 184, with the resilient sheet 186 in a nonstretched condition. As best seen in FIG. 10, a plurality of diagonally extending slits 188 are cut through tubular sheet 186. The sheet 186 and tubular wire screen 184 are mounted within the sleeve member 10% as by axial retaining elements 190.

When the sleeve l00b is stationary, slits 188 are closed, because of the unstretched condition of the resilient sheet 186. When the sleeve 10% is assembled in the centrifuge, upon operation of the centrifuge, the fluid is centrifugally forced outwardly against sheet 186 and the sheet is stretched or outwardly bulged in its extent between the ribs 182. The outwardly bulging or stretching action of the sheet causes the slits 188 to open, thereby permitting the heavier particles to OPERATION The centrifuge shown in the drawings, although capable of use in other environments, was specifically designed for removing contaminants from the lubricating oil system of a jet engine. Engines of this type employ a recirculating or'closed lubricating oil system; the centrifuge of the present invention having its inlet connected to receive oil after it has passed through the bearing parts of the engine, and having its outlet connected to return purified oil to the. supply side of the engine lubrication system. The. overall lubrication system itself has not been disclosed or described in detail because it may take any of several conventional forms. However, it will be understood that the centrifuge of the present invention may be connected into a recirculating lubrication system at any convenient point such that during operation of the system a continuous flow of contaminated lubricating oil is fed into the centrifuge inlet and a continuous flow of decontaminated lubricating oil is returned into the recirculating system from the centrifuge outlet.

The disclosed centrifuge operates to separate both cntrained air and other gases and two types of solid particles from the lubricating oil. The first type of solid particle may be considered to be ordinary dirt, primarily in the form of metal particles generated by wearing of the bearing surfaces and other rubbing or sliding parts in the engine. A second form of solid particle contaminant is produced from the lubricating oil itself or from the synthetic additives in the oil by the high pressures and temperatures to which the oil is exposed while performing its lubricating function. This latter type of particle is far more prevalent in closed lubrication systems of the general type under consideration and removal of this latter type of particle has been found to substantially prolong engine bearing life.

Contaminated oil from the lubrication system is, during operation of the engine, continuously fed into inlet conduit 74 into inlet chamber 70. As explained above, during operation of the centrifuge, the pump 128 operates at a flow rate which is at least equal to the rate of flow of contaminated fluid into chamber 70.

The high speed rotation of shaft 64, combined with the flow rate of the incoming fluid through chamber 70 forms an air pocket in the central portion of chamber 70 at the left-hand end (FIG. 1) of passage 78, while the oil and contaminant particles tend to flow within an annular region closely adjacent the walls of inlet chamber 70, thereby accomplishingan initial separation of entrained air and other gases from the incoming contaminated mixture.

The denser liquid and solid particles flow from inlet chamber 70 through the radially outwardly and axially rear wardly directed impeller passages 98 into the separation chamber in the interior of shell 80, entering the chamber with a tangentially and axially rearwardly directed flow component. The centrifugal action of the rotating shell and an nular sleeve 100 centrifugally urges the denser elements of the mixture radially outwardlythrough annular screen (of the FIG. 1 embodiment) into the particle-entrapping sleeve I00.

Desirably, the path of flow of the mixture from impeller passages 98 through the separation chamber is confined to a relatively radially narrow annulus. It will be noted that the flow is positively confined during its initial portion by the annular skirt I22. Desirably, the radially inner surface of the annular flow path should lie on a generally cylindrical surface spaced radially inwardly of screen 110 by an amount sufficient to provide an adequate cross-sectional area of flow at an axial flow rate consistent with the volume requirements of the circulating lubricating system and particle separation efficiency.

Decontaminated fluid which passes axially from the open right-hand end of sleeve 80 into themain internal chamber 44 is continuously withdrawn from chamber 44 by the pump 128 at a rate such that the flow of liquid through the shell 80 is confined to the relatively thin annulus described above. Vanes 126 function to maintain a constant rotary velocity of fluid within the annular flow path.

It will be appreciated that in all three of the embodiments of particle-entrapping sleevesi.e. the embodiments of FIGS. 1, 8 and 10both particles and lubricatingoil flow into the annular region between the inner surface of the sleeve and its outer wall. Desirably, as far as the contaminant particles are concerned, this centrifugally induced flow should be a oneway flow so that particles can move into the sleeve, but not back out of it. Further, it is desirable that flow of the mixture circumferentially within the interior of the sleeve be minimized to prevent slump" or settling of the mixture to the bottom of the sleeve when the centrifuge is stopped. In the wire mesh screen-fibrous material annulus embodiment of FIG. 1, the fibers tend to entrap the particles and inhibit movement of the particles circumferentially when the centrifuge is stopped. The wire mesh screen will permit reverse flow of the liquid, however, the entrapping fibrous material exerts a greater retaining action on the solid particles.

In the embodiment of FIG. 8, the sleeve tends to function as a sponge, and the centrifugal forces urging the particles into the porous entrapping material during operation of the centrifuge are far greater than the gravitational forces exerted on the particles when the centrifuge is stopped.

In the sleeve structure of FIG. 10, the slits in the resilient sheet material function as a valve which is opened while the centrifuge is in operation and closed when the centrifuge is stopped. Slump is inhibited in the FIG. embodiment by the longitudinal ribs.

All three forms of sleeve are of relatively simple and inexpensive construction and may be readily removed for cleaning and replacement.

While various embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that the disclosed embodiments may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting, and the true scope of the invention is that defined in the following claims.

lclaim:

l. A centrifugal separator for separating solid particles from a liquid-solid mixture comprising a casing having an internal chamber, an open-ended hollow cylindrical shell mounted in said casing for rotation about its axis within said internal chamber, drive means for driving said shell in rotation about its axis, the interior of said shell defining an annular separation chamber opening axially into said internal chamber, inlet means operable during rotation of said shell to continuously supply a tangentially and axially directed flow of a liquid-solid mixture to be separated into and axially through said separation chamber into said internal chamber, particle collecting means in said cylindrical shell adjacent the radially outer periphery of said separation chamber for receiving and entrapping solid particles from said mixture during its flow through said separation chamber, and pump means in said easing driven by said drive means for exhausting liquid from said internal chamber at a rate at least equal to the rate at which said mixture is supplied by said inlet means.

2. A separator as defined in claim 1 wherein said particle collecting means includes means for inhibiting movement of particles collected therein.

3. A separator as defined in claim 2 wherein said particle collecting means comprises an annular cylindrical sleeve detachably mounted within said cylindrical shell, said sleeve having an imperforate outer wall, and said means for inhibiting movement comprises a tubular particle-entrapping element seated upon and covering the inner surface of said outer wall.

4. A separator as defined in claim 3 wherein said tubular entrapping element comprises an annular body of porous cellular material.

5. A separator as defined in claim 3 wherein said entrapping element comprises a cylindrical wire mesh screen fixedly mounted on said outer wall in concentrically inwardly spaced relationship thereto to constitute an inner wall of said sleeve, and an annular body of fibrous material filling the space between said inner and outer walls.

6. A separator as defined in claim 3 wherein said entrapping element comprises a tubular sleeve of resilient sheet material having a plurality of slits therethrough, means supporting said sleeve in an unstretched condition in a radially inwardly spaced coaxial relationship to said outer wall, said slits being closed when said sleeve is in said unstretched condition and being opened upon stretching of said sleeve under the centrifugal force of liquid passing therethrough during rotation of said cylindrical shell to permit the passage of particles through the slits of said sleeve.

7. A centrrfugal separator for separating solrd particles from a fluid-solid mixture comprising a casing having an internal chamber, a shaft mounted for rotation about its axis within said internal chamber, drive means for driving said shaft in rotation, a cylindrical shell having an end wall at one end fixedly mounted upon said shaft for coaxial rotation therewith, said shell and said end wall defining an annular separation chamber surrounding said shaft with said separation chamber closed at its axially forward end by said end wall and opening into said internal chamber at its axially rearward end. inlet means operable during rotation of said shaft to supply a fluidsolid mixture to be separated into the forward end of said separation chamber and to impel the mixture radially outwardly into the separation chamber with an axially rearwardly directed flow component, annular sleeve means coaxially and detachably mounted within said cylindrical shell adjacent the radially outer periphery of said separation chamber for receiving and entrapping solid particles impelled thereto, and pump means in said casing driven by said drive means for pumping liquid from said internal chamber at a rate at least equal to the rate at which said mixture is supplied by said inlet means to said separation chamber.

8. A separator as defined in claim 7 wherein said inlet means comprises an enlarged diameter section at the forward end of said shaft having an inlet chamber coaxially formed therein, means defining impeller passages inclined radially outwardly and axially rearwardly from the rearward end of said inlet chamber into the forward end of said separation chamber, and an air vent passage extending rearwardly through said shaft along the axis thereof from said inlet chamber.

9. A separator as defined in claim 7 wherein said particle collecting means includes means for inhibiting movement of particles collected therein.

10. A separator as defined in claim 9 wherein said particle collecting means comprises an annular cylindrical sleeve detaehably mounted within said cylindrical shell, said sleeve having an imperforate outer wall, and said means for inhibiting movement comprises a tubular particle-entrapping element seated upon and covering the inner surface of said outer wall.

11. A separator as defined in claim 9 wherein said tubular entrapping element comprises an annular body of porous cellular material.

12. A separator as defined in claim 9 wherein said entrapping element comprises a cylindrical wire mesh screen fixedly mounted on said outer wall in concentrically inwardly spaced relationship thereto to constitute an inner wall of said sleeve, and an annular body of fibrous material filling the space between said inner and outer walls.

i3. A separator as defined in claim 9 wherein said entrapping element comprises a tubular sleeve of resilient sheet material having a plurality of slits therethrough, means supporting said sleeve in an unstretched condition in a radially inwardly spaced coaxial relationship to said outer wall. said slits being closed when said sleeve is in said unstretched condition and being opened upon stretching of said sleeve under the centrifugal force of liquid passing therethrough during rotation of said cylindrical shell to permit the passage of particles through the slits of said sleeve. 

1. A centrifugal separator for separating solid particles from a liquid-solid mixture comprising a casing having an internal chamber, an open-ended hollow cylindrical shell mounted in said casing for rotation about its axis within said internal chamber, drive means for driving said shell in rotation about its axis, the interior of said shell defining an annular separation chamber opening axially into said internal chamber, inlet means operable during rotation of said shell to continuously supply a tangentially and axially directed flow of a liquid-solid mixture to be separated into and axially through said separation chamber into said internal chamber, particle collecting means in said cylindrical shell adjacent the radially outer periphery of said separation chamber for receiving and entrapping solid particles from said mixture during its flow through said separation chamber, and pump means in said casing driven by said drive means for exhausting liquid from said internal chamber at a rate at least equal to the rate at which said mixture is supplied by said inlet means.
 2. A separator as defined in claim 1 wherein said particle collecting means includes means for inhibiting movement of particles collected therein.
 3. A separator as defined in claim 2 wherein said particle collecting means comprises an annular cylindrical sleeve detachably mounted within said cylindrical shell, said sleeve having an imperforate outer wall, and said means for inhibiting movement comprises a tubular particle-entrapping element seated upon and covering the inner surface of said outer wall.
 4. A separator as defined in claim 3 wherein said tubular entrapping element comprises an annular body of porous cellular material.
 5. A separator as defined in claim 3 wherein said entrapping element comprises a cylindrical wire mesh screen fixedly mounted on said outer wall in concentrically inwardly spaced relationship thereto to constitute an inner wall of said sleeve, and an annular body of fibrous material filling the space between said inner and outer walls.
 6. A separator as defined in claim 3 wherein said entrapping element comprises a tubular sleeve of resilient sheet material having a plurality of slits therethrough, means supporting said sleeve in an unstretched condition in a radially inwardly spaced coaxial relationship to said outer wall, said slits being closed when said sleeve is in said unstretched condition and being opened upon stretching of said sleeve under the centrifugal force of liquid passing therethrough during rotation of said cylindrical shell to permit the passage of particles through the slits of said sleeve.
 7. A centrifugal separator for separating solid particles from a fluid-solid mixture comprising a casing having an internal chamber, a shaft mounted for rotation about its axis within said internal chamber, drive means for driving said shaft in rotation, a cylindrical shell having an end wall at one end fixedly mounted upon said shaft for coaxial rotation therewith, said shell and said end wall defining an annular separation chamber surrounding said shaft with said separation chamber closed at its axially forward end by said end wall and opening into said internal chamber at its axially rearward end, inlet means operable during rotation of said shaft to supply a fluid-solid mixture to be separated into the forward end of said separation chamber and to impel the mixture radially outwardly into the separation chamber with an axially rearwardly directed flow component, annular sleeve means coaxially and detachably mounted within said cylindrical shell adjacent the radially outer periphery of said separation chamber for receiving and entrapping solid particles impelled thereto, and pump means in said casing driven by said drive means for pumping liquid from said internal chamber at a rate at least equal to the rate at which said mixture is supplied by said inlet means to said separation chamber.
 8. A separator as defined in claim 7 wherein Said inlet means comprises an enlarged diameter section at the forward end of said shaft having an inlet chamber coaxially formed therein, means defining impeller passages inclined radially outwardly and axially rearwardly from the rearward end of said inlet chamber into the forward end of said separation chamber, and an air vent passage extending rearwardly through said shaft along the axis thereof from said inlet chamber.
 9. A separator as defined in claim 7 wherein said particle collecting means includes means for inhibiting movement of particles collected therein.
 10. A separator as defined in claim 9 wherein said particle collecting means comprises an annular cylindrical sleeve detachably mounted within said cylindrical shell, said sleeve having an imperforate outer wall, and said means for inhibiting movement comprises a tubular particle-entrapping element seated upon and covering the inner surface of said outer wall.
 11. A separator as defined in claim 9 wherein said tubular entrapping element comprises an annular body of porous cellular material.
 12. A separator as defined in claim 9 wherein said entrapping element comprises a cylindrical wire mesh screen fixedly mounted on said outer wall in concentrically inwardly spaced relationship thereto to constitute an inner wall of said sleeve, and an annular body of fibrous material filling the space between said inner and outer walls.
 13. A separator as defined in claim 9 wherein said entrapping element comprises a tubular sleeve of resilient sheet material having a plurality of slits therethrough, means supporting said sleeve in an unstretched condition in a radially inwardly spaced coaxial relationship to said outer wall, said slits being closed when said sleeve is in said unstretched condition and being opened upon stretching of said sleeve under the centrifugal force of liquid passing therethrough during rotation of said cylindrical shell to permit the passage of particles through the slits of said sleeve. 